2005. 8. 4. Thurs / Current 김성민

[현중]

At night, the cities all over the world give out a bright shines. Every civilization could have been developed for the climate has been constant. But 10,000 years ago, the temperature on earth had been changed shakily. Then the temperature change came to a sudden stop and there has been no deviation(편차) even of 1° for recent 10,000 years. What makes the temperature be constant for 10,000years and be changed before then? It's the effect of deep sea current(심해해류). Then, what is the deep sea current and how can it control the temperature of the earth?

Norway coast(노르웨이 해안) is 10° higher than Siberia or Canada which are in the same latitude(위도) as it. It's all because of the Gulf stream(멕시코 난류) which passes by this coast.
Most of the current system(해류체계) is occurred by wind and this kind of system is formed. So by this theory, the Gulf stream can't flow into the Norway coast. But it flows. What is the reason?

In nineteen fifties, it happened to research the location of fallout(방사성 낙진). To be surprised, only in the North Atlantic, it was spreaded into under the 3000m of the sea. It meant that in the North Atlantic, there's local sediment movement(침강운동) of sea water.
If you put a cake of ice into the water, the surface water goes to the ice and when it touches the ice, it sinks under the water. It's because that the colder the water is, the bigger density(밀도) is and the heavier the water is. With the same theory, we can see that sediment movement, which is occurred by the difference of the water temperature rise in the "sea".
The temperature is not the only thing to change the density of the water. As sea water becomes more salty, its density becomes bigger. Then the enormous water columns(물기둥) are formed to the bottom of the sea. As enormous amount of sea water get submerged to the bottom, to fill the blank, sea water in another place goes to this place and the big movement of this sea water is the Gulf stream. So to speak, the North Atlantic which get cold by the glacier and originally salty sinks and to fill that place, the Gulf stream comes to flow.

At greenland coast in midwinter, as the surface of the water(수표면) fully freeze, sea water which become colder with bigger density pours down in the form of water column. A diameter(지름) of water column is at least hundreds meter and at most 1km. A hundreds of water columns suck up tremendous amount of water, which is the same bulk(부피) with 100 of "the Amazon River". If these water columns arrive at the bottom of the sea, it changes the direction and keep flowing under the 1000m of the sea. This is the very true form of the deep sea current. From then, this deep sea current runs along the America coast toward the Southern part(남단) of the Atlantic(대서양). About this time, the width of the deep sea current reaches to 100km.
The deep sea current is occurred not only in Atlantic but in Antarctic Marine(남극해). As water columns formed in Antarctic Marine flow together, the deep sea current get bigger and are divided into two parts at the Antarctica(남극대륙). One goes to the Indian Ocean(인도양) and another to the Pacific(태평양). A stream in the Pacific rushes to the New Zealand coast, where the deep and enormous trench(해구) is located. It is the North Pacific(북태평양) where the deep sea current stops in the end.
Then, do you know how much time it needs for this deep sea current to arrive at the North Pacific from the Greenland? It's as long as 2000 years. So if we have a water taken out of the North Pacific, it would have been submerged when Jesus was born.
This deep sea current rises to the surface of the water at the Indian Ocean and the Pacific and goes back to the Greenland coast under the effect of various current system. This large scale movement of sea water is called Oceanic Conveyor Belt(대양대순환해류). Oceanic Conveyor Belt runs all over the earth restlessly and cool the tropic sea and heat the cold sea. It's kind of enormous thermostat(온도조절장치) all over the whole earth.

Do you remember that I have said the temperature of the earth has been constant for the last 10000 years? That is because this Oceanic Conveyor Belt has maintained its stable condition. But Oceanic Conveyor Belt doesn't always maintain its stable statements continuously. What was the problem?

Let me put the focus on 13,000years ago, when our ancestors had had to suffer from a sudden cold. It's revealed that the temperature of the North Atlantic was very low at that time. The fact that water temperature  goes down in a sudden means that the Gulf Stream doesn't flow as the sinking stream(침강류) of the North Atlantic becomes weaker. Oceanic Conveyor Belt was stopped 13,000 years ago. Did what make such accident?
13,000 years ago, the earth was at the end of the ice age(빙하기). As the ice of the North America was about to melt off, transcendental lake of fresh water(민물) was formed inside the continent. As it became hotter, the ice wall around the lake crumbled down and tremendous amount of fresh water rushed upon the North Atlantic. As a result, salt density went down all of a sudden. If salt density went down, the sinking stream couldn't be formed. So Oceanic Conveyor Belt didn't work at all.
With Oceanic Conveyor Belt stopping, the severe cold(혹한) rushed for all over the earth. But the real problem was not the climate itself. It was the change of environments. Just as the plant was disappeared and soil had changed, harvest of the crops was devastated.

And 10,000 years later, Oceanic Conveyor Belt started working again and warm temperature came back. However, lately, Oceanic Conveyor Belt has a problem again.
The iceberg(빙산) is a floating lump of fresh water on the sea. Once the iceberg starts melting, salt density becomes lower. Recently the number of the iceberg is increasing very rapidly by accelerated global warming(온난화 현상).
If global warming is continued, the evaporation rate(증발량) at equatorial sea area(적도해역) jumps up. As air is filled with the moisture too much, precipitation(강수량) is increased very much and the rain is centered mostly on Siberia and Canada. As a result, a water level(수위) of river which flows to the Arctic Ocean(북극해) and the Atlantic goes up higher. Then it makes salt density decreased, which results in imbalance of deep sea current like 13,000years ago.
According to data, by global warming, convection(대류) of deep sea stream will be weakened rapidly in the early part of the 21c. And in the middle part of 21c, it will be dropped to the 2/3 level of the present degree.
It can be possibly true that Oceanic Conveyor Belt comes to a stop like 13,000years ago by sudden global warming. One thing for sure is that if it is so, there will be unimaginable, radical climate change on earth.
However, most of all, weakening of sinking stream is the real problem because if the change us gradual, human being can be accustomed to the change. It will be all right if only we change the farming method or kinds of crops. But if we can't anticipate the degree at weakening of sinking stream, everything will be over just wondering what should be planted, how much it will rain and how much it will shine.

The stable condition of Oceanic Conveyor Belt for the last 10,000 years was a surprising miracle. But we are breaking a extremely delicate balance of nature by occurring global warming. The mild climate for 10,000 years which enables human being to develop all the civilization wholly depends on large scale of deep sea stream under the 3000 of the sea. The miracle of Oceanic Conveyor Belt, which needs as long as 2000years for one circulation! Now, people are scarcely aware of the fact that every things on earth are based on extremely subtle harmony and balance.